Grooved dryer

ABSTRACT

The method and apparatus for drying moist traveling paper webs in a high speed papermaking machine wherein the dryer drums have peripheral surfaces provided with narrow venting grooves in particular configuration to facilitate air and steam ventilation carried over the dryer drum surface by the oncoming paper web.

United States Patent 1191 Ely June 11, 1974 GRQOVED DRYER" 3,429,256 2/1969 Balleau 29/121 R 5] Inventor: onal A. y o e, I". v3,445,938 5/1969 Clarlr 34/116 [73] Assignee: Beloit Corporation, Beloit, Wis. primary bh J Camby 1 22 F] d: v M 12, 1973 Assistant Examiner-James C. Yeung 1 l e M Attorney, Agent, or Firm-Dirk J. Veneman; Bruce L. pp 339,741 Samlan; Gerald A. Mathews [52] US. Cl .1 34/111, 34/116, 34/123 57 ABSTRACT [51] Int. Cl. ......F26b 11/02 58 Field of Search 34/110, 111, 116, 123; The method a apparatus drying "M11118 34/240, 243 F; 226/91196; 29/121 R, 121 Papefiwebs 2 Speed P machme A 121 H wherein the dryer drums have penpheral surfaces provided with narrow venting grooves in particular con [56] References Cited figuration to facilitate air and steam ventilation carried overthe dryer drum surface by the oncoming I UNITED STATES PATENTS paper web. I 3,198,697 8/1965 Justus 29/121 R 3,405,855 lO/l968 Daly et al.

3 Claims, 7 Drawing Figures PATENTEDJUH] 1 I974 3,815,256

sum 20F 2 DRY CREPED TISSUE KRAFT MACHINE GLAZED SURFACE/HR.

w P b L co m {IIIT lllll KRAFT PAPER llllllllllwlllll O 20 4O 6O 80 I00 I20 I40 DRYER EQUIVALENT STEAM PRESSURE (RS.I.)

FIG

40 FIG. 5

ER/SQ.

LBS. PAP

. 1 GROOVED DRYER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to papermaking and more particularly is directed to new and improved methods and means for removing moisture from a traveling paper web in a dryer section.

2. BriefDescription of the Prior Art In modern day paper drying mechanisms, a traveling paper web is generally passed sinuously up and down between upper and lower tiers ofdryer drums with-an upper and lower felt guided by guide rolls holding the web onto the respective surfaces of the heated dryer drums. As the web approaches the dryer drum air is carried onto the dryer drum surfaces by the oncoming paper web. This air thus entrapped builds up a layer of air under pressure between the web and the dryer surface causing not only poor heat transfer to the web but also causing the traveling web to float, wrinkle, break or otherwise deviate from its path of travel to the detriment of efficient operation. In addition, as the web is dried, vaporizationof the moisture in the web takes place causing a vapor cushion to beformed between the dryer surface and the web, thereby tending to lift the web out of contact with the heated dryer surfaces and thereby further retarding efficient dryer operatrons.

SUMMARY OF THE INVENTION It is an important object of the instant invention to provide an improved method and apparatus for drying a moist paper web.

It is another object of the instant invention to provide a dryer drum having means providing more intimate contact between a moving paper web and the dryer drum surface.

It is a further object of the instant invention to provide a dryer drum having means for providing greater surface area on the drum surface for additional heat transfer to a paper web in contact therewith.

Other objects, features and advantages of the instant invention will become more apparent from the following detailed description of the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a graphical representation of drying rates for paper as a function of dryer steam pressure;

F IG. 4 is an enlarged partial elevational view of the structure shown in FIG. 2; and

FIG. 5 is an enlarged partial sectional view of a portion of a dryer cylinder constructed in accordance with the present invention.

FIG. 6 is an essentially schematic view illustrating a groove configuration provided on a dryer drum surface in accordance with the principles of the instant invention;

FIG. 7 is another schematic view illustrating another groove configuration utilized on a dryer drum surface in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIG. 1, a traveling paper web W, such as is received'from a press section of a papermachine, is guided by means of an idle roll 11 into the dryer section, generally indicated .at 10, to be carried over a series of cylindrical dryer drums illustratedin sequence at 12, 13, 14 and '15. While only a portion of the dryer section is shown, the web W will pass sequentially in serpentine fashion over moredryer drums until a desired degree of dryness is obtained. I

The dryer drums are arranged in tiers, with the upper tier being represented by dryer drums 12 and 14 and the lower tier by dryer drums 13 and 15. The dryer drums are suitably heated, as indicated diagrammatically at H, and include means for heating the outer periphery of the dryer drum surface via axial feed or heating fluid to the respective inner peripheries of the drying drums. In addition, other suitable. heating means may be provided.

The web W travels at a speed determined by the speed of rotation of the various dryer drums andsev- ,eral means (not shown) can be provided for driving the dryer drum at predetermined speeds. Generally, each of the dryer drums are interconnected and driven at controlled speeds as will be appreciated by those skilled in the art, and such mechanisms need not be discussed further. 1

The traveling web W is guided and held onto the individual dryer drum peripheral surfaces by dryer felts F-l and F-2. Generally, the felts F-l and F-2 are formed of a porous material and may be of any type of fabric which will allow air and steam to pass through it. The felts may also be formed of plastic fabric or screen. A suitable material being a foraminous plastic screen or fabric of the type known as Formex" fabric,-which permits moisture vapor to be driven through the fabric by heated air. The web W alternately travels around the rolls l2 and 14 of the upper tier and the rolls 13 and 15 of the lower tier.

As shown in detail in FIG. 2 as the web W approaches the drying cylinder 12, a substantial amount of air (indicated by small arrows) is trapped between the web W and the outer periphery of the drying cylinder 12. This entrapped air causes'the web W to be separated from the drying cylinder surface and results not only in loss of traction but more importantly in a substantial loss of heat transfer. As the felt F-l contacts the paper web and urges the web towards the dryer periphery the air space between the web and the dryer periphery is somewhat diminished but due to evaporation of moisture from the web W this space is never entirely eliminated since it is difficult for the evaporated moisture to travel through the paper web W and the felt F-l.

The detrimental effect of this layer of air between the web W and the drying surface of the drying cylinder can be best illustrated with reference to FIG. 3. FIG. 3 is a graphical representation showing pounds of paper dried per square foot of dryer surface per hour as a function of the 'dryer equivalent stream pressure in psi. In order to fully appreciate the significance of this graphical representation it should be understood that dry creped tissue as well as kraft machine glazed paper is dried by forcibly pressing the moist web against the surface of a polished drying cylinder. This paper thus pressed onto the cylinder surface remains in firm contact therewith throughout a substantial portion of its circumference so that there is no possibility of an insulating layer of air being built up between the paper web and the dryer surface. Kraft paper on the other hand, is dried in the conventional manner, that is, in the manner illustrated in FIG. 1. It should further be appreciated that the weight per 3,000 square feet of kraft machine glazed paper and the weight per 3,000 square feet of kraft paper are for all practical purposes similar. It will thus be noted from the graphical representation of FIG. 3 that for an equivalent steam pressure of psi, 3.4 lbs. of kraft machine glazed paper can be dried per square foot of dryer surface per hour whereas only 1.0 lbs. of kraft paper can be dried with the equivalent dryer surface and in the same amount of time. The difference of 2.4 lbs. of paper dried at the same steam pressure between kraft machine glazed paper and kraft paper are thus substantial.

ln practicing the principles of the instant invention it is therefore attempted to approach the drying rate of kraft machine glazed paper as nearly as practicable but it should become immediately apparent that a slight improvement in heat transfer rate will result in substantial savings. For example, if by partially eliminating the insulating layer of air between the web and the surface of the drying cylinder the number of pounds of paper dried can be raised (at 10 psi) from 1 lb. to 1.6 lbs., the overall efficiency of that particular dryer section will have been raised by 60 percent which is a substantial saving.

As illustrated in FIGS. 6 and 7, the dryer drums are provided with a plurality of circumferentially alternating grooves and ridges and certain configurations. The grooves may be in the form of continuous spiral extending over the entire drum periphery. The helically grooves may be relatively opposed defining diamondshaped land areas on the peripheral surface of the dryer drums. The relatively narrow uniformly spaced grooves act as venting means to purge air carried over the dryer drum surface by the oncoming paper web, and also to vent moisture vapor which forms between the dryer drum surface and the web during the drying process. The venting of this air and steam permits more intimate contact of the web with the dryer drum surface thereby greatly facilitating more efficient heat transfer to the web and allowing better traction between the web and the dryer drum surface so that the web does not wrinkle, break or otherwise deviate in its path of travel around the periphery of the drum. With the peripheral grooves of the present invention, the intimate contact between the dryer surface and the paper web is further enhanced by a sucking action of air flowing out of the grooves at high speed and in a direction opposite to the direction of web travel. This is clearly illustrated in FIG. 4.

As shown in FIG. 4, air enters the grooves at approximately the web velocity as indicated by the arrows A and rapidly fills up the groove space. At a point B the groove is filled with air and pressure starts to build up resulting in an outward flow of air as indicated by the arrows C. Due to an increase in the temperature of the air as it enters the groove this pressure buildup is quite rapid and the velocity of the outflowing air C is larger than the velocity of the ingoing air A. This outward rush of air C creates a vacuum condition in the remaining groove space indicated at D by virtue of which the web W is urged towards the roll periphery thereof enhancing the web-to-dryer surface contact and increasing the drying rate.

In addition, the grooves also provide more actual surface area on the dryer surface, thereby allowing greater heat transfer from the heated, dryer drum to the contacting web. The plurality of alternative grooves and ridges may be directly cut or machined onto a dryer drum surface with appropriate means, or the drum surface may be so formed in the manufacturing process thereof. Further, in certain instances, it has been found that suitable drum sleeves or covers can be formed from an appropriate heat conductive heat material, such as stainless steel or aluminum, with the grooves and ridges being formed on the sleeve and then the sleeve can be appropriately fitted over a plain surface dryer drum. This approach is particularly advantageous where the shell thickness of existing dryer drums is too thin to permit the cutting of relatively deep grooves into the dryer drum periphery.

The preferred grooved dryer drum 40 is shown in fragmentary detail in FIG. 5, and the grooves 41 are shown as having a substantially uniform axially dimension 42, which is substantially in the range of 0.025 to 0.200 inch between generally cylindrical smooth land areas or ridges 44 having an axial dimension 45 that is substantially in the range of 0.1 to 2.0 inch. The grooves are thus defined between generally radially extending parallel sidewalls substantially to the bottom 46 thereof which may be rounded with a radius of about one-half the groove width 42. This groove construction accommodates a sufficient volume of air and steam while at the same time eliminating structural stresses (because of unfavorable stress concentration in sharp corners) and facilitates cleaning or venting of the grooves since there are no corners present where fuzz or other like material can accumulate.

It has been found that it is generally desirable and necessary to provide sufficient land area to fully support the traveling paper web, providing a generally solid surface for contacting the same, while at the same time providing grooves having sufficient volume (as a function of the cross sectional area) to receive and vent all of the air and steam vapor entrapped by the oncoming web and carried over the drum surface, which are nevertheless sufficiently narrow to allow theweb to bridge the same without marking the web.

Experimental studies have indicated that the minimum groove depth should be approximately 0.015 inch, the minimum groove width should be approximately 0.030 inch and the maximum lead of a spiral groove or the distance between grooves in the event that annular grooves are used should be approximately 2 inches. On the other hand, experiments have indicated that the maximum depth should be preferably not exceed 0.200 inches, this dimension being largely governed by stress considerations of the most commonly used drying shells. The maximum width should preferably not exceed 0.200 inches since an excessive width may cause marking of the paper web while the minimum lead should preferably not be less than 0.1 to 0.5 inches.

it will be seen from the foregoing that a new and improved drying method and apparatus has been provided to greatly increase the efficiency and drying operations involving paper webs. The grooved dryer drums of the present invention facilitate more intimate contact between the web and the dryer surface by purging air and steam carried out to the dryer surface by the oncoming web.

The drawings and specification present a detailed disclosure, of the preferred embodiments of the invention, but it will be understood that the invention is not limited to the specific form disclosed and covers all modifications, changes and alternative constructions and methods falling within the scope and principles taught by the invention.

Having thus described the invention, what is claimed l. A high speed web drying apparatus for paper machines including:

a plurality of heated dryer drums arranged in an upper and lower tier,

a web traveling successively around dryer drums of the upper and lower tier,

upper and lower felts of pervious material which allow gaseous fluids to pass therethrough,

guide rolls positioned between the dryer drums of each tier for guiding the felts against the respective dryer drums in the upper and lower tiers with the web therebetween,

said drums having peripheral surfaces provided with a web traction means to urge the traveling web toward said dryer surfaces thereof enhancing the web-to-dryer surface contact to prevent deviation of the web from its normal path around said dryer surfaces, 1

said traction means comprising a plurality of alternating generally circumferentially aligned grooves and ridges wherein a portion of each groove has a vacuum zone by virtue of the velocity of the air flowing out of the groove being greater than the velocity of the air flowing into the groove.

2. A high speed web drying apparatus for paper machines in accordance with claim 1, wherein:

the grooves have an axial dimension at the groove periphery substantially in the range of from 0.025 to 0.200 inches and extend generally radially inward for a distance substantially in the range of from 0.015 to 0.200 inches along generally parallel sidewalls, said sidewalls terminating in a bottom portion having a radius one-half of the groove width and the ridges each present a generally circumferentially outer peripheral land area having an axial dimension substantially in the range of from 0.1 to 2.0 inches at the roll periphery.

3. A high speed web drying apparatus for paper machines in accordance with claim 1, wherein:

the web traction means on the peripheral surfaces of the dryer drums provide a relatively greater surface area on said surfacesfor increased heat transfer from said dryer surface to the traveling web. 

1. A high speed web drying apparatus for paper machines including: a plurality of heated dryer drums arranged in an upper and lower tier, a web traveling successively around dryer drums of the upper and lower tier, upper and lower felts of pervious material which allow gaseous fluids to pass therethrough, guide rolls positioned between the dryer drums of each tier for guiding the felts against the respective dryer drums in the upper and lower tiers with the web therebetween, said drums having peripheral surfaces provided with a web traction means to urge the traveling web toward said dryer surfaces thereof enhancing the web-to-dryer surface contact to prevent deviation of the web from its normal path around said dryer surfaces, said traction means comprising a plurality of alternating generally circumferentially aligned grooves and ridges wherein a portion of each groove has a vacuum zone by virtue of the velocity of the air flowing out of the groove being greater than the velocity of the air flowing into the groove.
 2. A high speed web drying apparatus for paper machines in accordance with claim 1, wherein: the grooves have an Axial dimension at the groove periphery substantially in the range of from 0.025 to 0.200 inches and extend generally radially inward for a distance substantially in the range of from 0.015 to 0.200 inches along generally parallel sidewalls, said sidewalls terminating in a bottom portion having a radius one-half of the groove width and the ridges each present a generally circumferentially outer peripheral land area having an axial dimension substantially in the range of from 0.1 to 2.0 inches at the roll periphery.
 3. A high speed web drying apparatus for paper machines in accordance with claim 1, wherein: the web traction means on the peripheral surfaces of the dryer drums provide a relatively greater surface area on said surfaces for increased heat transfer from said dryer surface to the traveling web. 